Such tool chucks and their freely movable locking members have the advantage of great simplicity over conventional arrangements using spring-loaded or pivoted gripping claws (e.g. German Pat. Specn. No. 1 246 967).
A chuck of the specified kind has already been proposed in which the locking members are sliding blocks that are movable in a purely radial direction (British magazine "Machines & Tooling", 1974, No. 2, Page 35, Figure 3c). When forced inwardly, projections on the sliding blocks extending radially inwards engage a collar formed on the tang of the tool. Release of the tool is effected by virtue of the contacting faces of the projections and the collar having sloping wedge faces which generate a radial thrust for displacing the sliding blocks when an axial load acts on the tool. In cross section, the sliding blocks are cylindrical for the purpose of keeping the cost of machining the blocks as well as their ways within reasonable bounds. However, it is clearly necessary to prevent the sliding blocks from turning in their slideways to ensure that the intended face of each block will in fact engage the tang of the tool. Moreover, in this prior arrangement the sliding blocks must be provided with stop faces to prevent them from dropping out of their ways when there is no tool in the chuck. For these reasons as well as because of the necessary provision of inclined faces production is complicated and rather expensive.
Another drawback of this known form of construction is that the inclined faces apply considerable radial forces and tilting moments to the sliding blocks and their ways so that they are liable to jam and to suffer considerable wear.
It is an object of the present invention to provide a tool chuck of the specified kind which is reliable in operation, which is less liable to wear, and which is also inexpensive to produce.
According to the invention, this is achieved by features wherein the locking members have the basic shape of circular segments each located with its circularly arcuate edge facing radially inwards, part of the edge being slidable in slots on faces of complementary shape and at least part being adapted to engage the tang at the end of the tool shank.
The locking members have a configuration that is easy to produce. For instance, several locking members may be associated in a full circle and their circularly arcuate edges jointly machined at the same time. The slideways respectively slots can also be easily produced by discshaped milling cutters.
Release by the locking members is effected by their circular sliding movement about the notional center of the arcuate edge.
According to the invention, part of the circularly arcuate edge projecting radially inwardly through the locating slot is arranged to engage the tang of the tool. More particularly, this may be formed with a neb which positively engages recesses formed in the tang of the tool. During the releasing motion, this neb swings away from the tang and thus permits the tool to be withdrawn. The contacting surfaces between the neb and the collar formed on the tang are preferebly normal to the spindle axis, a feature which also facilitates machining the locking members and the tang on the taper shank of the tool.
Moreover, in order to bring about the locking movement, the edges of the locking members which face radially outwardly have a cam contour which slopes outwards in releasing direction for engagement by the control sleeve when the draw-in rod is retracted and thus to force the locking members inwards again.